Significantly improved peak rates of 1 Gbps in the downlink and 500 Mbps in the uplink are required for a Long Term Evolution-Advanced (LTE-A) system as compared to a Long Term Evolution (LTE) system. Also good compatibility of the LTE-A system with the LTE system is required. The technology of Carrier Aggregation (CA) is introduced to the LTE-A system to accommodate the required improved peak rates, compatibility with the LTE system and full use of frequency resources.
The CA technology refers to presence of a plurality of Component Carriers (CCs) in both the uplink and the downlink in a cell instead of a mode in which there is only one pair of component carriers in the LTE system and earlier wireless communication systems. A base station (eNB) manages and schedules uniformly a plurality of sets of component carriers in the cell. The component carriers may be consecutive or inconsecutive, and the maximum bandwidth of each component carrier is 20 MHz for compatibility with the LTE system.
From the perspective of a User Equipment (UE), the user equipment can receive downlink data and scheduling information concurrently over a plurality of downlink component carriers and transmit uplink data and feedback information regarding downlink transmission over a plurality of uplink component carriers.
In the CA mechanism, common points of the downlink layer 2 and the upper layer 2 of the LTE-A system to those of the LTE system lie in the following points.
The Packet Data Convergence Protocol (PDCP) and the Radio Link Control (RLC) layer are the same in structure as those of the LTE system; and the Medium Access Control (MAC) layer function is the same as that of the LTE system and primarily performs scheduling, including priority and resource allocation, etc., on a user equipment.
Different points lie in the following points.
There is a separate Hybrid Automatic Repeat Request (HARM) entity for each component carrier; each component carrier corresponds to a separate transmission channel; and a Transport Block (TB) is organized separately for each component carrier, and no component carrier can be exchanged through retransmission.
Typically, a user equipment transmits uplink data and receives downlink data according to dynamical scheduling from the network side. As meant by dynamical scheduling, each time the user equipment is intended to transmit and receive data, dynamical scheduling signaling is transmitted from the network side to the user equipment over a Physical Downlink Control Channel (PDCCH), and the user equipment transmits and receives the data over a resource indicated in the dynamical scheduling signaling upon reception of the dynamical scheduling signaling.
In order to reduce an overhead of signaling, the LTE system introduces Semi-Persistent Scheduling (SPS) for a service with substantially the same size and a regular arrival interval of data packets and specifies that one user equipment can be configured with only one set of SPS resources.
Semi-persistent scheduling refers to a user equipment is configured with a period of semi-persistent scheduling and a Semi-Persistent Scheduling Cell Radio Network Temporary Identifier (SPS C-RNTI) in advance by the network side and semi-persistent scheduling signaling is transmitted to the user equipment from the network side, and the user equipment detects the semi-persistent scheduling signaling for the user equipment according to the configured SPS C-RNTI and then transmits and receives data over a resource indicated in the semi-persistent scheduling signaling at an interval of the configured period of semi-persistent scheduling.
The user equipment is configured with the period of semi-persistent scheduling and the used SPS C-RNTI by a Radio Resource Control (RRC) entity and the semi-persistent scheduling signaling is transmitted to the user equipment over a PDCCH.
There is only one component carrier of the LTE system, and without spatial multiplexing, a user equipment can transmit only one TB in a sub-frame, so if the user equipment receives dynamic PDCCH scheduling signaling of a sub-frame while there is an SPS resource allocation in the sub-frame, the user equipment can only transmit data in the sub-frame in response to an instruction in the dynamic scheduling signaling while disregarding the SPS resource allocation.
The inventors have identified during making of the invention the following technical problems in the prior art.
With the introduction of the CA mechanism, a user equipment can transmit data concurrently over a plurality of component carriers in a sub-frame, and at least one TB can be borne over each CC. In this case, if the user equipment is scheduled from the network side to perform uplink transmission including both SPS transmission and dynamical scheduling transmission in the sub-frame, a specific implementation has been absent so far to how the user equipment transmits data in the time unit in response to scheduling from the network side.